Control system for ignitron tubes



Dec. 26, 1950 G, J. ,LEXA 2,535,499

' CONTROL SYSTEM FORIGNITRON TUBES Filed June 29,1949

If 1 p T lo Patented Dec. 26, 1950 i 2,535,499 CONTROL SYSTEM FORIGNITRON TUBES George J. Lexa, Wauwatosa, Wis., assignor toCutler-Hammer, Inc., Milwaukee, Wis., a, corporation of DelawareApplication June 29, 1949, Serial No. 101,992

5 Claims.

, This invention relates to a control system for ignitron tubes.

In certain control systems for ignitron tubes, the ignition voltage forenergizing the ignition electrode thereof is supplied by energy storedin a capacitor. The capacitor is charged with alternating voltagethrough a rectifier from a source of alternating current and the energystored therein is discharged through the ignition electrode and cathodeof the ignitron to initiate its conduction. Charging of the capacitor isusually effected during non-conducting periods of the ignitrons anddischarged during the conducting periods thereof. In certainapplications of ignitrons the moment of initiation of conduction thereofwill vary widely. Under certain load conditions it is necessary tcinitiate conduction of the ignitrons just prior to the end of theconducting half cycles of voltage impressed on said ignitron, whereasunder extreme load conr ditions, the ignitron is made conducting at, orjust after the beginning, of the conducting half cycles of voltageimpressed theeron. Regardless of the condition of loading the capacitorsupplying the ignition energy is charged to a potential such that itwill discharge during substan-' tially the entire conducting half cycleof voltage impressed on said ignitron. Thus under the extreme conditionsof loading aforementioned,

while the capacitor in discharging decreases in potential, the chargingvoltage impressed thereon is such as to recharge it during the periodsof its discharge. This causes the flow of unnecessary high currentthrough the ignition electrode and cathode of the ignitron, such currentex- ,ceeding considerably in amount that required maximum value has.been reached, so as a conse- Lq'uence thereof the energy dischargedthrough' the, ignition electrode and cathode of the ignitron "issubstantially only that stored in' said capacitor prior to the momentthe ignitron is rendered conducting.

An object or the present invention is to pro 'yide an energizing systemfor ignitron tubes reistricting to a minimum the required ignitionenergy; and

j Another object is to provide a system of the 2 aforementioned typewhich afl'ords a substantially constant amount of ignition energyregardless of the loading on the ignitron tube.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates one embodiment of the inventionwhich will now be described, it being understood that the embodimentshown is susceptible of modification in re spect of its details withoutdeparting from the scope of the appended claims.

In the drawing: I r

.Figure 1 illustrates, partly diagrammatically and partly schematically,a control system for a polyphase alternating current motor.

Fig. 2 illustrates the relationship of voltage existing between certaincomponents of the control system of Fig. 1 under one operatingcondition, and

Fig. 3 is similar to Fig. 2 but illustrates the relationship of voltagesunder another operating condition. 1

Referring to Fig. 1; it shows a three phase alternating currentinduction motor I 0 having a primary winding w and a secondary windinglo Winding Ill is providedwith three terminals T T and T Terminals T andT are directly connected to the bus bars L and L of a threephasealternating supply circuit. A pair of ignitron tubes H and 22 areconnected between bus bar L of the current suppl circuit and terminal Tof the motor primary in an inverse parallel relation. More particularlycathode ll of tube I! and anode H of tube !2 are connected to terminal'I while anode H of tube H and cathode iZ of tube l2 are connected tobus bar L Ignitron tubes II and 12 are provided with .ignitor electrodesH and 12 respectively, which when suitably energized initiate conductionof the respective tubes.

The circuit arrangement of the main electrodes of tubes II and 12 in thepower supply to the motor It is like that shown and described in theElliot Patent 2,448,256, issued August 31, 1948. The purpose of thetubes II' and I2 when the conduction thereof is suitably controlled-bythe control system to be described hereinafter in detail, is thatdescribed in the aforementioned patent. Although in the aforementionedpatent the motor corresponding to motor it is shown as having secondaryresistance which is controlled,

such is dispensed with in the present application as it forms no part ofthe present invention.

through a resistor 31.

disclosed in the aforementioned patent may be incorporated with thesecondary winding lil of the motor Iii if desired.

A preferred system for controlling the conduction of ignitrons ii and I2will now be described.

A transformer 13, schematically depicted in Fig. l, is provided with alaminated core 83 and a primary winding 53 having one end terminalconnected to bus bar L and its other end terminal connected to bus bar Lthrough a winding M which is wound on a laminated core M of an inductivereactor M, which is also schematically depicted in Fig. 1. Transformeri3 has a secondary winding I3 having endterminals l5 and I6. Endterminal 15 of winding l3 is connected to an anode li of a thyratrontube I! through a half-wave rectifier l8 and resistors l9 and 20.

The end terminal E6 of winding I3 is connected.

to the cathode H of ignitron i l. A capacitor 2| is connected at oneofits terminals to a common point between the resistors 59 and 2B andits'other terminal is connected to a point common to terminal is ofwinding l3 and cathode II" of ignitron ll. Cathode ['1 of thyratron H isconnected to the ignitron electrode H' of ignitron H. Thyratron l! isalso provided with a control electrode ll which is connected to thecathode li through a smoothing capacitor 22.

Transformer I3 is also provided with another secondary winding l3 havingend terminals 23 and 24. End terminal 23 of winding 13 is connected toanode 22.5 of a thyratron tube 25 through a half-wave rectifi'er26 andresistors 21 and 28. End terminal 24 of'winding' 13 is connected to thecathode [2 of ignitron i2. Acapacitor 29 is connected at one terminal toa point common to the resistors 21 and 28 and is connected at its otherterminal to a point. common to end terminal 2 of winding 13 and cathodeiz 'of ignitron l2. Cathode 25 of thyratron 25 is connected to theignitor electrode l2 of ignitron IZ. Thyratron 25 is also provided witha control electrode 25 which is connected to the cathode 25 thereofthrougha smoothing capacitor30.

A transformer 31 is provided with a primary winding 3 l having oneof'its terminals connected to bus bar L and its other end terminalconnected to bus bar L Transformer 3! also has a secondary winding 3|having end terminals 32 and 33 and a mid-point terminal 34. End terminal33 is connected to the terminal 34 through a variable inductance 35 anda primary winding 33 of a transformer 36. End terminal 32 is connectedto a point common to the inductance 35 and the winding 36 of transformer36 Transformer 36 is also provided with a secondary winding 36 havingend terminals38 and 39 andanother secondary winding it having endterminals 40v and. 4|. The terminal 39 of winding 36 is connected tocontrol electrode 1'! of thyratron H' through a resistor 42 and theterminall38 or; said winding is connected to a point common to. thecathode ill of'thyratron ll and the capacitor 22-. The terminal 4Bof'winding 36 is connected'to control electrode 25' of thyratron25through a resistor 43 and the terminal 4! ofsaid' windingis' connectedto a' point common to the cathode 25 of thyratron 25 and the capacitor30.

As will be understood by thoseskilled in the art, transformer 3!,variable inductance 35, and resistor 31 constitutes a phase shiftnetwork of a well known type. The output of such network is impressed onthe control electrodes 1'! and 25 of thyratron I! and 25 respectively,through the medium of the secondary windings 3t and 36 of transformer36. Any other suitable adjustable phase shift network may be used in theplace of the one herein shown and described. In the aforementionedpatent there is shown a phase shift network which is particularlysuitable when it is desired to automatically afiord adjustments thereofaccording to variations in operating conditions of the motor.

It has been found in connection with the present control system that forbest operation when the phase shift network is adjusted for maximumphase shift, the voltage impressed on the control electrode I! shouldlag the voltage impressed on the anode ll 'of ignitron H not less than30 and similarly the same relation should exist between the voltagesimpressed on the control electrode 25 of thyratron 25 and on the anode(2 of ignitron II.

It has also been found that for best operation of the present controlsystem, under no load conditions, the voltages induced in the secondarywinding la should lead the voltage impressed on the anode li of ignitronH by and similarly that the same relation should exist between thevoltages induced in secondary winding l3 of transformer 93 and thatimpressed on the anode [2 of ignitron 52.

To best understand the advantages of the present control system, itsoperation will be first considered as if the reactor M were not'includedin the power connections to the primary winding il of transformer i3 andthen its operation will be considered with such reactor included as hereinbeforeshown and described.

In the first case the voltage induced in the secondary winding l3 willhave the usual sinusoidal wave form as depicted by the dotted line curveA in Fig. 2. When the polarity of the voltage at the terminal 55 ispositive with respect to that at the terminal is in winding I3 currentWill flow through the rectifier l8, resistor l9, capacitor 2| toterminal l6 thereby charging capacitor 2: to the potential depicted bythe straight line B in Fig. 2. At the moment the charge on capacitor 2!has reached the potential B, the voltage impressed on the anode li ofignitron H becomes positive; the voltage impressed on the anode li beingdepicted by the curve C in Fig. 2. Assuming that the aforedescribedphase shift network is adjusted for maximum phase shift, then thevoltage impressed on the control electrode li of thyratron Il may bethat depicted by the curve D in Fig. 2. When the voltage impressed oncontrol electrode ll exceeds the critical potential of thyratron [1,which is represented by the straight line E in Fig: 2, thyratron I? willconduct. As a result of thyratron I1 becoming conducting, capacitor 2|discharges through a path including resistor 20, thyratron H, theignitor H and cathode H of ignitron ll, thereby initiating conduction ofthe'latter which remains conducting for the remainder'of the half cycleof anode voltage depicted by the curve C; the moment of initiation ofconduction of ignitron I! being depicted by the vertical line F in Fig.2.

Although capacitor 2! may be such that when charged to the potential Band discharged as aforedescribed to initiate conduction of ignitron H,current in excess of that supplied from the capacitor will also flowthrough the discharge path aforementioned. At the moment thyratron IT isrendered conducting the polarity of the enemas voltage at terminal f ofwinding 13 is still positive with respect to terminal l=6 andsof suchmagnitude that current flows. through rectifier -t'8gresistor I 9supplementing the current flowing through the discharge path fromcapacitor 21'. Such excess current is proportional to the "area underthe curve A to the right of vertical line F. As such excess current isnot needed for initiating conduction of ignitron ll, its only effect isto shorten the life of ignitor electrode I I. As the phase shiftnetworkxis adjusted more towarda condition of minimum phase shift, such'as depicted by the relationship of voltages shown in Fig. 3, the amountof such excess current decreases, and at the condition of phase "shiftdepicted, no excess current will flow through the discharge path ofcapacitor 2|. found-that the average current "supplied to the It hasbeen lgnitor of ignitron tube l'l under 'a condition of maximum phaseshift is 5 to 6 times that supplied under a condition of minimum phaseshift.

Now considering the present control system as it actually exists withthe reactor l4 connected .in the power connections to the primarywinding 13 of transformer l3, the relationship of the instantaneousvoltages induced in the winding l3, when terminal 15 thereof is positivewith respect to its terminal 16, is not of sinusoidal wave form but isof the high peaked forms to zero rapidly and attains a zero value beforethe anode voltage of ignitron H is of sufficient magnitude to render thelatter conducting.

Therefore the only current supplied through the aforementioned dischargepath of capicitor 2! is that stored in the latter, there being no excesscurrent supplied from the winding l3. When the phase shift network isadjusted to provide a condition near minimum phase shift net, depictedby Fig. 3, the wave form of the voltage induced in winding I3 changessomewhat to that depicted by curve G and leads the anode voltage ofignitron II by substantially 90. It has been found that when the voltageinduced in winding l3 has the wave forms depicted by curves G and Gunder the conditions of phase shift depicted by Figs. 2 and 3, theaverage ignitor current is the same for both conditions, and the samefor other conditions of phase shift therebetween. Thus with the presentcontrol system the ignitor ll is supplied with only that amount ofenergy as is necessary to initiate conduction of ignitron H and the lifeof the latter is thereby materially enhanced.

The wave form of the voltages induced in winding I? will also be likethat depicted by curves G and G of Figs. 2 and respectively. Thusignit-ron 12, which is controlled in exactly the same manner as ignitronII during positive half cycles of the voltage impressed on its anode [2will likewise be supplied with only that amount of energy needed toinitiate its conduction.

It has been found by experiment that by using an inductive reactorhaving acore formed of electrical sheet steel laminations describing aclosed magnetic path and with its inductance winding connected in thepower connections to the primary winding as hereinbefore described,voltages will be induced in the secondary windings of the transformerhaving wave .forms generally similar to those depicted by curves G and Gin Figs. 2 and 3 respectively. In one particular embodiment of thepresent control system, wave forms of the voltages induced in thesecondary windings of the transformer 13 were obtained which weresubstantially like that depicted by curves G and G using the followingcombination of a transformer and inductive reactor connected asaforedescribed to a 215 volt alternating supply source: Transformer:

Rating-335 volt amperes Primary winding-240 turns of #IQDCwire Secondarywinding-316 turns (each) of #24DC wire Coreformed of electrical sheetsteel laminations describing closed magnetic path Inductive reactor:

Inductance winding-430 turns of #HI'ZE wire I Core-formed of electricalsheet steel laminations describing a closed magnetic path suitable for avolt-ampere transformer As will be understood by those skilled in theart, the combinations of transformers and reactors that will provideinduced voltages having wave forms substantially like the wave formsdepicted by curves G and G depends upon a number of variables. Generallyconsidered, when the primary Winding of the transformer and theinductance winding are connected in circuit as hereinbefore describedand the secondary windings of the transformer are open circuited, themeasured voltage drops across the primary winding of the transformer andacross the inductance winding of the reactor should be substantiallyequal.

1 claim:

1. In combination, an alternatin current supply source, an ignitron tubewhich through its main electrodes conducts energy from said source andwhich has an ignitor electrode. means, including a capacitor, supplyingenergy stored in said capacitor to said ignition electrode in timedrelation to the voltage cycles of said source, transforming andrectifyiue means in energy supplying relation to the first mentionedmeans includin said capacitor, and a primary circuit for saidtransforming means supplied from said source and having reectanceaffording peaking of the voltage pulses in the secondary of saidtransforming means restricting transfer of en ergv to said ignitorelectrode from said source substantially to only the energy stored insaid capacitor.

2. In combination, an alternating current supply source, an ignitrontube which through its main electrodes conducts energy from said sourceand which has an ignitor electrode, means, including a capacitor,supplying energy stored in said capacitor to said ignition electrode intimed relation to the voltage cycles of said source, an inductivereactor, a rectifier, a transformer having its primary winding connectedto said source through the winding of said reactor and having itssecondary winding connected to said capacitor through said rectifier,said transformer and said reactor in association affording peaking ofthe voltage pulses in the secondary winding of said 7 transformer forrestricting transfer of energy to said ignitor electrode from saidsource substantially to only the energy stored in said capacitor;

3. In combination, an alternating current supply source, an ignitrontube which through its main electrodes conducts energy from said sourceand which has an ignitor electrode, means, including a capacitor,supplying energy stored in said capacitor to said ignition electrode intimed relation to the voltage c cles of said source, an inductivereactor having a core formed of a low reluctance material and describinga closed mag-- netic path upon which its winding is wound, a rectifier,a transformer having its primary winding connected to said sourcethrough the Winding of said reactor and having its primary windingconnected across said capacitor through said rectifier, said transformerand said reactor in association aifording peaking or the voltage pulsesin said transformer secondary winding for restricting transfer of energyto said ignitor electrode from said source substantially to only theenergy stored in said capacitor.

4. In combination, a polyphase alternating current supply source, atranslating device connected to said source for deriving energytherefrom, an ignitron tube having its main electrode connected in apower connection to said device and having an ignitor electrode, means,including a capacitor, supplying energy stored in said capacitor to saidignitor electrode, means limiting the supply of energy to said ignitorelectrode in a timed relation to conducting half cycles of voltage ofsaid ignitron tube, an inductive reactor having a core formed of a lowreluctance material and describing a closed magnetic path upon which itswinding is wound, a rectifier, and a transformer having its primarywinding connected across one phase of said source through the windin ofsaid reactor and having its sec ondary Winding connected across saidcapacitor through said rectifier, said transformer and said reactor inassociation affording peaking of the voltage pulses in the transformersecondary winding for restricting transfer of energy to said ignitorelectrode from said source substantially to only the energy stored insaid capacitor.

5. In combination, a polyphase alternating current supply source, atranslating device connected to said source for deriving energytherefrom, an ignitron tube having its main electrodes connected in apower connection to said device and having an i-gnitor electrode, acapacitor, a normally non-conducting second electron tube having itsmain electrodes connected across said capacitor through said ignitorelectrode and the cathode of said ignitron tube and having a controlelectrode, an inductive reactor having a core formed of a low reluctancematerial and forming a closed magnetic path upon which its winding isWound, a rectifier, a transformer having its primary winding connectedacross one phas of said source through the winding of said reactor andhaving its secondary winding connected across said capacitor throughsaid rectifier for charging said capacitor during the non-conductingperiods of said ignitron tube, and means deriving energy from saidsource of supply to said control electrode and limiting to theconducting half cycles of voltage of said ignitron tube the supply ofenergy to initiate discharge of said capacitor through said second tubefor energizing said ignitor electrode, said transformer and said reactorin association affording peaking of the voltage pulses in saidtransformer secondary winding for restricting the transfer of energy tosaid ignitor electrode from said source to substantially only the energystored in said capacitor.

GEORGE J. LEXA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,306,230 Somerville Dec. 22,1942 2,422,575 Marsh et al June 17, 1947 2,444,921 Dawson et al. July13, 1948 2,{i48,256 Elliot Aug. 31, 1948

